.alpha.-olefin polymers, particularly ethylene polymer and an ethylene-.alpha.-olefin copolymer have generally been prepared by a known process wherein ethylene is polymerized, or ethylene and an .alpha.-olefin are copolymerized under the presence of a titanium-based catalyst comprising a titanium compound and an organoaluminum compound or a vanadium-based catalyst comprising a vanadium compound and an organoaluminum compound.
A new series of Ziegler catalysts comprising a zirconium compound and an aluminoxane have also been recently proposed for polymerization of an olefin.
Japanese Patent Application Kokai No. 58-19309 describes a process for polymerizing ethylene and at least one C.sub.3 -C.sub.12 .alpha.-olefin at a temperature of from -50.degree. to 200.degree. C. under the presence of a catalyst comprising a transition metal-containing compound represented by the formula: EQU (cyclopentadienyl).sub.2 MeRHal
wherein R is selected from cyclopentadienyl, C.sub.1 -C.sub.6 alkyl, and halogen, Me is a transition metal, and Hal is a halogen,
a linear aluminoxane represented by the formula: EQU Al.sub.2 OR.sub.4 (Al(R)--O).sub.n
wherein R is methyl or ethyl, and n is a number of 4 to 20, and
a cyclic aluminoxane represented by the formula: ##STR1## wherein R and n are as defined above. It is also described that ethylene should be polymerized in the presence of a small amount, that is, up to 10% by weight of an .alpha.-olefin having a somewhat longer chain or the mixture thereof to adjust a density of the resulting polyethylene.
Japanese Patent Application Kokai No. 59-95292 describes processes for preparing a linear aluminoxane represented by the formula: ##STR2## wherein n is a number of 2 to 40 and R is a C.sub.1 -C.sub.6 alkyl, and a cyclic aluminoxane represented by the formula: ##STR3## wherein n and R are as described above. It is also disclosed that at least 25 million grams of polyethylene may be produced per 1 g of transition metal per hour when an olefin is polymerized in the presence of a mixture of, for example, methylaluminoxane prepared as described above and a bis(cyclopentadienyl) compound containing titanium or zirconium.
Japanese Patent Application Kokai 60-35005 discloses a process for preparing an olefin-polymerization catalyst comprising effecting a reaction between a magnesium compound and an aluminoxane compound represented by the formula: ##STR4## wherein R.sup.1 is a C.sub.1 -C.sub.10 alkyl radical, and R.sup.0 may represent R.sup.1 or, taken together, form --O--; chlorinating the reaction product; and treating the product with Ti, V, Zr, or Cr-containing compound to produce an olefin-polymerizing catalyst. It is also disclosed that this catalyst is particularly preferable for copolymerizing ethylene with a C.sub.3 -C.sub.12 .alpha.-olefin.
Japanese Patent Application Kokai No. 60-35006 discloses a catalyst system for polymers blended in a reactor which comprises a combination of (a) a mono-, di- or tri-cyclopentadienyl compound of at least two different transition metals, or a derivative thereof, and (b) an aluminoxane. Example 1 of this application discloses that a polyethylene having a number average molecular weight of 15,300, a weight average molecular weight of 36,400, and propylene content of 3.4% may be prepared by polymerizing ethylene and propylene by using bis(pentamethylcyclopentadienyl)zirconium dimethyl and an aluminoxane as catalyst. Example 2 discloses that a blend of polyethylene and ethylene-propylene copolymer having a number average molecular weight of 2,000, a weight average molecular weight of 8,300, and propylene content of 7.1 mol % and comprising a toluene-soluble portion having a number average molecular weight of 2,200, a weight average molecular weight of 11,900, and propylene content of 30 mol % and a toluene-insoluble portion having a number average molecular weight of 3,000, a weight average molecular weight of 7,400, and propylene content of 4.8 mol % may be prepared by polymerizing ethylene and propylene by using bis(pentamethylcyclopentadienyl)zirconium dichloride, bis(methylcyclopentadienyl)zirconium dichloride, and an aluminoxane as catalyst. Example 3 discloses a blend of LLDPE and ethylene-propylene copolymer comprising a soluble portion having a molecular weight distribution (Mw/Mn) of 4.57 and propylene content of 20.6 mol %, and an insoluble portion having a molecular weight distribution of 3.04 and propylene content of 2.9 mol %.
Japanese Patent Application Kokai No. 60-35007 describes a process for polymerizing ethylene either alone or together with an .alpha.-olefin having at least 3 carbon atoms under the presence of a catalyst containing a metallocene and a cyclic aluminoxane represented by the formula: ##STR5## wherein R is an alkyl radical of 1 to 5 carbon atoms and n is as described above. The polymer prepared by such a process has a weight average molecular weight of about 500 to about 1,400,000 and a molecular-weight distribution of 1.5 to 4.0.
Japanese Patent Application Kokai No. 60-35008 discloses that a polyethylene or an ethylene-C.sub.3-10 .alpha.-olefin copolymer having a wide molecular-weight distribution may be prepared by using a catalyst system containing at least two metallocenes and an aluminoxane. There is also disclosed that the copolymer has a molecular-weight distribution (Mw/Mn) of 2 to 50.
Japanese Patent Application Kokai Nos. 60-260602 and 60-130604 disclose processes for polymerizing an olefin by utilizing catalysts comprising a transition metal compound and mixed organoaluminum compounds of an aluminoxane and organoaluminum compound. These patent applications disclose that polymerization activity per unit weight of the transition metal can be increased by adding the organoaluminum compound. However, these processes suffered from a defect that the catalysts required a large amount of expensive aluminoxane, and the activity per unit weight of the aluminoxane was still low.
The catalysts comprising a transition metal compound and an aluminoxane as proposed in the above-mentioned patent applications are provided with a significantly superior polymerization activity compared to the conventional catalyst systems prepared from a transition metal compound and an organoaluminum compound. These catalysts, however, are mostly soluble in the reaction system, and frequently require adoption of solution polymerization system, resulting in a significantly increased viscosity of the polymerization-system solution. Moreover, the polymers produced by subsequently treating with these solution systems have low bulk density, and therefore, polymers having excellent powder properties have been quite difficult to obtain.
On the other hand, attempts have been made to polymerize an olefin in dispersion or gas-phase polymerization systems by using catalysts wherein one or both of said transition metal compound and said aluminoxane are supported on a porous carrier of an inorganic oxide such as silica, silica-alumina, and alumina.
For example, aforementioned Japanese Patent Application Kokai Nos. 60-35006, 60-35007 and 60-35008 disclose that the transition metal compound and the aluminoxane supported on a carrier such as silica, silica-alumina, and alumina can also be used as catalysts.
Japanese Patent Application Kokai Nos. 60-106808 and 61-106809 disclose a process for preparing a composition comprising a polyethylene-based polymer and a filler which involves preliminarily contacting a high-activity catalyst component containing titanium and/or zirconium which is soluble in a hydrocarbon solvent with a filler, and then polymerizing ethylene or copolymerizing ethylene and an .alpha.-olefin in the presence of the thus treated catalyst component, an organoaluminum compound, and a filler which has an affinity for a polyolefin.
Japanese Patent Application Kokai No. 61-31404 discloses a process for polymerizing ethylene or copolymerizing ethylene and an .alpha.-olefin in the presence of a mixed catalyst comprising a transition metal compound and a product obtained by reacting a trialkylaluminum and water under the presence of silicon dioxide or aluminum oxide.
Japanese Patent Application Kokai No. 61-276805 discloses a process for polymerizing an olefin in the presence of a catalyst comprising a reaction mixture between an inorganic oxide containing surface hydroxyl radical such as silica and a reaction mixture obtained by reacting a zirconium compound and an aluminoxane with a trialkylaluminum.
Japanese Patent Application Kokai Nos. 60-108610 and 61-296008 disclose a process for polymerizing an olefin in the presence of a catalyst comprising a transition metal compound such as a metallocene and an aluminoxane supported on a carrier such as an inorganic oxide.
However, when an olefin is polymerized or copolymerized in a dispersion or gas-phase polymerization system by utilizing the solid catalyst components supported on a carrier as mentioned above, polymerization activity is markedly reduced and the properties inherent to the catalyst comprising the transition metal compound catalyst component and the aluminoxane catalyst component are not fully exerted. Powder properties such as bulk density of the thus prepared polymer were also insufficient.